Geographic data relates to data concerning the topography of a specific geographic region, and this data may include geodetic data and non-geodetic data. Geodetic data refers to geographic data that is stored in an angular coordinate system (such as, for example, latitude and longitude information) that is geo-referenced to the earth's surface. Non-geodetic data includes geographic data that has been projected to a “flat” map.
It is generally known to overlay rectilinear shaped cells, typically in the form of a straight-lined grid pattern, overtop of a surface map displaying geographic features, and then to store geographic data related to the geographic features along with associated cell IDs in a database. The each cell ID is a unique cell identifier for a particular rectilinear shaped cell.
Information retrieval systems are then used to retrieve specific stored geographic data in response to query requirements issued by a user. Typically the sort of surface maps having overlaid rectilinear-shaped grids have the north pole represented as a straight line along the top peripheral border of the surface map and the south pole represented as another straight line along the bottom peripheral border of the surface map, while the 180th Meridian (formerly the International Date Line matched up with the 180th Meridian but no longer) is used as the peripheral border of the sides of the surface map.
A rectilinear shaped cell is bounded by, or characterized by, a straight line or lines formed into a box-like shape which may include a square shaped cell (that is, a plane figure having four equal sides), or a shape having an equal-sided rectangular form, or some shape having one or more right angles, or a figure having four right angles (a rectangular figure twice as long as it is wide which may have a set of mutually perpendicular axes that meet at right angles).
To access a large volume of geographic data, an index is used. Ideally, the index should permit the information retrieval system to access stored geographic data quickly and efficiently. For a given query, the index should be used in a seamless manner, even for cases when the query includes a region of interest (that is, a given subset of the mosaic of rectilinear shaped cells) that spans across the polar regions of the globe (that is, across the peripheral edges or borders of the surface map). The region of interest may span across the International Date Line (that is, the side borders of the surface map). At present, the information retrieval system may examine parts of the database that are related to the rectilinear shaped cells which are not of interest because these cells happen to be placed between the polar regions. Therefore time would be wasted on these sorts of queries that attempt to search across peripheral borders.
Accordingly, a solution is desired that addresses, at least in part, these shortcomings.